Withdrawal of priming fluid from extracorporeal circuit of hemodialysis

Abstract

A method for withdrawing priming fluid from the extracorporeal circuit of a dialysis machine is described which substantially prevents return of the priming fluid back to the patient. In accordance with the method, priming fluid is drawn from the extracorporeal circuit through the dialyzer membrane and into the dialysate circuit. Blood is introduced into the extracorporeal circuit as the priming fluid is withdrawn through the dialyzer. Withdrawal of the priming fluid may be accomplished by pumping the blood pump in the forward direction at a first rate and operating a pump in the dialysate circuit at a second rate. Valves in the dialysate circuit are operated such that the pump in the dialysate circuit draws priming fluid across the dialyzer membrane into the dialysate circuit, and thereby prevents the priming fluid from being returned to the patient. In a preferred embodiment, the fluid volumes of the arterial and venous portions of the extracorporeal circuit, and the fluid volume of the blood side of the dialyzer, are known in advance. With this information, it is possible to operate the blood and dialysate pumps such that the blood progresses into the arterial and venous lines at different rates such that blood reaches the dialyzer via both lines at about the same time, while at the same time the priming fluid is withdrawn through the dialyzer. Thus, in this embodiment, blood fills the extracorporeal circuit after priming with only a small amount of priming fluid remaining in the blood compartment of the dialyzer being returned to the patient.